Yep. I tried to guesstimate Steamroller's performance and failed miserably. I was off by a good 100%+ on IPC. The architecture is just so broken that what would normally be a huge improvement results in a headfirst slam into another bottleneck. At this point, the issue is either with the stupid high cache and memory access latencies, or the whole thing is unsalvageable.
I originally thought it could be salvaged as well. Looked like there was plenty of low hanging fruit. This turned out to be incorrect. I'm not sure if it was just a money/talent issue though - with the cutbacks in spending and layoffs, it just may not have been possible to get the kind of IPC gains that were so glaringly possible.
AMD is severely lacking in performance. 20nm provides more performance. New nodes are just as big of a deal as architecture updates, if not more so. 20nm is a bit of an outlier in this regard because of the somewhat higher cost, but the performance benefits are still there.
However, 20nm at GloFo is not a high performance process. The only flavor of 20nm they offer is 20nm Low Power Mobility.
This is definitely a money issue. AMD has decided to not fund additional research for higher performance nodes. The result was quite clear with Kaveri. At 4 GHz, this would have been a much more impressive chip.
As you point out, even if EX comes out on 20nm, it will still likely be frequency limited. And if it comes out on 28nm, there will definitely be a scaling back of features as has been AMD's pattern of late.
A tiny part of me has been hoping that the cutbacks on the 'dozer line of CPUs has been because Jim Keller has been socking away money to develop a new architecture for future big core AMD CPUs. Sadly, AMD's financials seem to against this and their partnership with GFL seems point against AMD being able to make a competitive mainstream CPU.
Mubadala could possibly put a bit of money into AMD to help them along until GFL has more high profile customers, but I doubt they would invest enough to make AMD competitive again (especially given AMD's debt load). This is at least as bad as watching the Alpha fade of into obscurity...